Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00750 (PLA)
 16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A 39-kDa protein copurifies with the low-density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP) and inhibits the binding and/or cellular uptake of ligands by this receptor. We recently utilized glutathione S-transferase (GST)-39-kDa fusion protein constructs to demonstrate that constructs encoding amino-terminal residues 1-114 and carboxy-terminal residues 115-319 of the 39-kDa protein independently bind to purified LRP and to LRP on hepatoma cells with similar affinities as the full-length GST-39-kDa protein (Kd approximately 8-10 nM). These regions, however, inhibit ligand binding to LRP differently: GST/1-114 inhibits both tissue-type plasminogen activator (t-PA) and alpha 2-macroglobulin-methylamine (alpha 2M*) binding whereas GST/115-319 only potently inhibits t-PA binding. Four domains, containing residues 18-24 and 100-107 within amino-terminal constructs and residues 200-225 and 311-319 within carboxy-terminal constructs, are required for inhibition of ligand binding. In the present study, we generated additional 39-kDa protein constructs to precisely define residues within each domain required for inhibition of t-PA and alpha 2M* binding to LRP. The potential importance of these residues in mediating direct binding both to purified LRP and to LRP on hepatoma cells was examined. Within amino-terminal residues 1-114, alanine 103 and leucine 104 are required for inhibition of t-PA and alpha 2M* binding. These residues, however, are not required for binding either to purified LRP or to LRP on hepatoma cells. Within domain 18-24, arginine 21 is required for inhibition of t-PA and alpha 2M* binding as well as for the direct binding of amino-terminal constructs to LRP. Within carboxy-terminal domains 200-225 and 311-319, leucine 222 and leucine 319 are both required for inhibition of t-PA binding. Deletion of leucine 319 changes the ligand specificity from inhibition of t-PA binding to inhibition of alpha 2M* binding. Thus, leucine 319 is not required for direct binding to LRP whereas leucine 222 is required for high-affinity binding to LRP.
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PMID:Sites within the 39-kDa protein important for regulating ligand binding to the low-density lipoprotein receptor-related protein. 753 37

The present study was undertaken in order to determine the recognition site for tissue-type plasminogen activator-plasminogen activator inhibitor type 1 [t-PA-PAI-1] complexes in rat liver in vivo and in vitro. After intravenous injection into rats t-PA-PAI-1 complexes were rapidly removed from the plasma and the liver took up 80% of the injected dose. Within the liver parenchymal and endothelial liver cells contributed mainly to the uptake of t-PA-PAI-1, and were responsible for 62% and 24% of the liver uptake, respectively. The interaction of t-PA-PAI-1 with isolated rat parenchymal liver cells was of high affinity (Kd 17 nM). A well-known antagonist of the alpha 2-macroglobulin receptor (alpha 2MR/low-density lipoprotein receptor-related protein (LRP), GST-39kDa protein (GST-39kDaP) efficiently inhibited the binding (IC50 0.7 nM) of t-PA-PAI-1 to rat parenchymal liver cells. The interaction of t-PA-PAI-1 with LRP on rat parenchymal liver cells was not Ca2(+)-dependent and is most probably mediated by a specific determinant on PAI-1, since an anti-PAI-1 monoclonal antibody inhibited the binding of t-PA-PAI-1, where as free t-PA did not. The binding of t-PA-PAI-1 to rat hepatocytes could not be inhibited by a complex of plasmin and alpha 2-antiplasmin nor by various other ligands of LRP like beta-VLDL and lactoferrin. Binding of t-PA-PAI-1 to rat parenchymal liver cells was followed by internalization and subsequent degradation in the lysosomal compartment. It is concluded that parenchymal and endothelial liver cells mediate the removal of t-PA-PAI-1 complexes from the circulation. LRP on rat parenchymal liver cells is responsible for the uptake and degradation of t-PA-PAI-1 and may therefore be important for the regulation of the t-PA levels in the circulation.
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PMID:Characterization of the interaction of a complex of tissue-type plasminogen activator and plasminogen activator inhibitor type 1 with rat liver cells. 860 13

The catabolism of the novel plasminogen activator reteplase (BM 06.022) was described. For this purpose BM 06.022 was radiolabelled with 125I or with the accumulating label 125I-tyramine cellobiose (125I-TC). BM 06.022 was injected at a pharmacological dose of 380 micrograms/kg b.w. and it was cleared from the plasma in a biphasic manner with a half-life of about 1 min in the alpha-phase and t1/2 of 20-28 min in the beta-phase. 28% and 72% of the injected dose was cleared in the alpha-phase and beta-phase, respectively. Initially liver, kidneys, skin, bones, lungs, spleen, and muscles contributed mainly to the plasma clearance. Only liver and the kidneys, however, were responsible for the uptake and subsequent degradation of BM 06.022 and contributed for 75% to the catabolism of BM 06.022. BM 06.022 was degraded in the lysosomal compartment of both organs. Parenchymal liver cells were responsible for 70% of the liver uptake of BM 06.022. BM 06.022 associated rapidly to isolated rat parenchymal liver cells and was subsequently degraded in the lysosomal compartment of these cells. BM 06.022 bound with low-affinity to the parenchymal liver cells (550 nM) and the binding of BM 06.022 could be displaced by t-PA (IC50 5.6 nM), indicating that the low-density lipoprotein receptor-related protein (LRP) could be involved in the binding of BM 06.22. GST-RAP, which is an inhibitor of LRP, could in vivo significantly inhibit the uptake of BM 06.022 in the liver. It is concluded that BM 06.22 is metabolized primarily in the liver and the kidneys. These organs take up and degrade BM 06.022 in the lysosomes. The uptake mechanism of BM 06.022 in the kidneys is unknown, while LRP is responsible for a low affinity binding and uptake of BM 06.022 in parenchymal liver cells.
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PMID:Uptake, internalization and degradation of the novel plasminogen activator reteplase (BM 06.022) in the rat. 877 28

Several clinical studies have demonstrated an inverse relationship between circulating levels of estrogen and tissue-type plasminogen activator (t-PA). The present study was designed to test the hypothesis that estrogens lower plasma levels of t-PA by increasing its clearance from the bloodstream. 17alpha-Ethinyl estradiol (EE) treatment resulted in a significant increase in the clearance rate of recombinant human t-PA in mice (0.46 mL/min in treated mice v 0. 32 mL/min in controls; P <.01). The clearance of endogenous, bradykinin-released t-PA in rats was also significantly increased after EE treatment (area under the curve [AUC], 24.9 ng/mL. min in treated animals v 31.9 ng/mL. min in controls; P <.05). Two distinct t-PA clearance systems exist in vivo: the low-density lipoprotein receptor-related protein (LRP) on liver parenchymal cells and the mannose receptor on mainly liver endothelial cells. Inhibition of LRP by intravenous injection of receptor-associated protein (RAP) as a recombinant fusion protein with Salmonella japonicum glutathione S-transferase (GST) significantly retarded t-PA clearance in control mice (from 0.41 to 0.25 mL/min; n = 5, P <.001) and EE-treated mice (from 0.66 to 0.35 mL/min; n = 5, P <.005), but did not eliminate the difference in clearance capacity between the 2 experimental groups. Similar results were obtained in mice in which LRP was inhibited via overexpression of the RAP gene in liver by adenoviral gene transduction. In contrast, administration of mannan, a mannose receptor antagonist, resulted in identical clearances (0.22 mL/min in controls and 0.24 mL/min in EE-treated mice). Northern blot analysis showed a 6-fold increase in mannose receptor mRNA expression in the nonparenchymal liver cells of EE-treated mice, whereas the parenchymal LRP mRNA levels remained unchanged. These findings were confirmed at the protein level by ligand blotting and Western blotting analysis. Our results demonstrate that EE treatment results in increased plasma clearance rate of t-PA via induction of the mannose receptor and could explain for the inverse relationship between estrogen status and plasma t-PA concentrations as observed in humans.
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PMID:Increased clearance explains lower plasma levels of tissue-type plasminogen activator by estradiol: evidence for potently enhanced mannose receptor expression in mice. 1043 21

Tissue-type plasminogen activator (t-PA), is a serine proteinase that catalyzes the initial and rate-limiting step in the fibrinolytic cascade. Its plasma activity is determined by the rate of release into the bloodstream, the rate of inhibition by plasminogen-activator inhibitor type 1 (PAI-1) and the rate of hepatic clearance. Two receptor systems contribute to the clearance of t-PA: the mannose receptor and the low-density lipoprotein receptor-related protein (LRP) that removes free t-PA as well as t-PA-PAI-1 complexes from the blood. During pregnancy a significant rise in the plasma levels of pregnancy zone protein (PZP) is observed, while alpha(2)-macroglobulin (alpha(2)-M) remains constant. Interestingly, the fibrinolytic activity is decreased during this period. In this context, we have recently demonstrated the in vitro formation of PZP-t-PA complexes. Here, we purified LRP from human placenta by affinity chromatography and then analyzed the binding specificity and affinity of PZP-proteinase complexes to the receptor by enzyme immunoassay (EIA). Our results clearly established that the binding of PZP-t-PA complexes to LRP was specific, saturable, and with K(d) = 337 +/- 31 nM. Moreover, by using the same EIA, we further observed that this binding was inhibited by receptor-associated protein. These data suggest that PZP, by binding to t-PA and promoting its clearance via LRP, might contribute in vivo to the downregulation of the fibrinolytic activity during pregnancy.
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PMID:Pregnancy zone protein-tissue-type plasminogen activator complexes bind to low-density lipoprotein receptor-related protein (LRP). 1133 11

Maspin is a novel serine protease inhibitor with tumor suppressive activity, inhibiting tumor invasion and metastasis. To date, the underlying molecular mechanism of maspin remains elusive. Recombinant maspin has been shown to specifically inhibit cell surface-associated urokinase-type plasminogen activator (uPA) and fibrinogen-bound tissue-type plasminogen activator. However, the role of endogenous maspin in plasminogen activation is totally unknown. To address this issue, we generated stable maspin-expressing transfectants using prostate carcinoma cells DU145 as the parental cell line. We report here that endogenous maspin exerts pleiotropic inhibitory effects on the pericellular uPA system. Maspin expression led to a significantly reduced level of cell surface-bound uPA and uPA receptor proteins without altering the steady-state levels of the respective mRNAs. Treatment with receptor-associated protein (RAP), a specific inhibitor of low-density lipoprotein receptor-related protein, lead to a significantly increased level of secreted uPA and cell surface uPAR in maspin transfectants but not in the mock control cells. A combination of enzymatic and molecular analyses revealed that maspin inhibits the cell surface-mediated plasminogen activation by forming an SDS-resistant complex with cell surface-bound uPA. In addition, maspin expression led to a dramatic reduction in the release of active uPA, both high molecular weight and the low molecular weight, into the conditioned culture medium. Consistently, the conditioned medium of maspin transfectant clones had a significantly reduced activity in converting plasminogen to plasmin. The inhibitory effect of maspin on pericellular uPA correlates with significantly decreased cell invasion potential and motility in vitro. The maspin-neutralizing antibody (Abs4A) reversed the subdued invasive potential of maspin transfectant cells in a dose-dependent manner. In summary, this study provides the first evidence that endogenous maspin is a potent inhibitor of pericellular uPA. Furthermore, our results support a current hypothesis that maspin blocks tumor invasion and motility by inhibiting localized pericellular proteolysis.
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PMID:Pleiotrophic inhibition of pericellular urokinase-type plasminogen activator system by endogenous tumor suppressive maspin. 1175 84

Plasminogen activator inhibitor 1 (PAI-1) inhibits plasminogen activators (u-PA and t-PA) by forming stable complexes endocytosed via a low-density lipoprotein receptor superfamily member-dependent mechanism. PAI-1 circulates actively in plasma and latently in platelets but is also secreted and deposited into the matrix by several cells, where it participates in tissue repair processes.
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PMID:Plasminogen activator inhibitor 1: physiological and pathophysiological roles. 1190 93

Tissue type plasminogen activator (tPA) is a key enzyme in the fibrinolytic cascade. In this paper we report that tPA contains 2 independent epitopes that exert opposite effects on blood vessel tone. Low concentrations of tPA (1 nM) inhibit the phenylephrine (PE)-induced contraction of isolated aorta rings. In contrast, higher concentrations (20 nM) stimulate the contractile effect of PE. The 2 putative vasoactive epitopes of tPA are regulated by the plasminogen activator inhibitor-1 (PAI-1) and by a PAI-1-derived hexapeptide that binds tPA. TNK-tPA, a tPA variant in which the PAI-1 docking site has been mutated, stimulates PE-induced vasoconstriction at all concentrations used. The stimulatory, but not the inhibitory, effect of tPA on the contraction of isolated aorta rings was abolished by anti-low-density lipoprotein receptor-related protein/alpha(2)-macroglobulin receptor (LRP) antibodies. Administering tPA or TNK-tPA to rats regulates blood pressure and cerebral vascular resistance in a dose-dependent mode. In other in vivo experiments we found that the vasopressor effect of PE is more pronounced in tPA knockout than in wild-type mice. Our findings draw attention to a novel role of tPA and PAI-1 in the regulation of blood vessel tone that may affect the course of ischemic diseases.
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PMID:In vitro and in vivo effects of tPA and PAI-1 on blood vessel tone. 1451 9

Axonal damage in multiple sclerosis (MS) lesions is associated with failure of fibrinolysis because of the inhibition of the plasminogen activator system. Plasma membrane receptors for tissue plasminogen activator (tPA) and plasminogen concentrate proteolytic activity on the cell surface and provide protection from inhibitors that in turn may locally enhance the fibrinolytic response. Therefore, we have investigated expression of two of these receptors in MS lesions, annexin II tetramer (AIIt) and low-density lipoprotein receptor-related protein (LRP). In acute MS lesions both AIIt and LRP were immunolocalized on macrophages and astrocytes while LRP was additionally found on neuronal cells in cortical gray matter. Western blot analysis confirmed a significant increase in AIIt in MS lesions and in a proportion of normal-appearing white matter samples, with a highly significant correlation between annexin II levels and factors associated with impeded fibrinolysis, such as plasminogen activator inhibitor-1. Immunoblotting analysis of plasmin(ogen) revealed increased levels of lysine-plasminogen in samples expressing high AIIt protein levels. Our results suggest that limited availability of tPA in MS lesions because of formation of tPA-plasminogen activator inhibitor-1 complexes reduces capability of tPA receptors to generate plasmin, which further diminishes fibrinolytic capacity in active MS lesions and possibly leads to axonal damage.
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PMID:tPA receptors and the fibrinolytic response in multiple sclerosis lesions. 1579 94

Although the mechanism of action of tissue-type plasminogen activator (tPA) in excitotoxic necrosis is well documented, whether this serine protease can influence the apoptotic cascade remains a subject of debate. Here, we report that tPA protects cultured cortical neurones against apoptotic cell death induced by serum deprivation, an effect associated with a reduction of caspase-3 activation. Interestingly, blocking tPA proteolytic activity by either tPA stop or neuroserpin did not prevent this neuroprotection. Similarly, prevention of the interaction between tPA and its receptor low-density lipoprotein receptor-related protein (LRP) could not alter tPA anti-apoptotic activity. Interestingly, the survival-promoting effect of tPA was blocked by the phosphatidylinositol-3 (PI-3) kinase inhibitor, LY294002, but not by the mitogen-activated protein (MAP) kinase inhibitor, U0126. In conclusion, the present demonstration of an anti-apoptotic effect of tPA, independent of its enzymatic activity, reveals an additional level of complexity in our understanding of this critical mediator of brain physiology and pathology.
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PMID:Tissue-type plasminogen activator rescues neurones from serum deprivation-induced apoptosis through a mechanism independent of its proteolytic activity. 1680 Aug 49


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